Abstract: Using software CFX 12.1, this paper investigated airflow patterns in the yarn suction gun with different geometrical parameters of the jet orifice by numerical simulation, and discussed the relation between the flow patterns and yarn suction performance. The affecting mechanism of jet orifice geometry on the yarn suction performance was clarified and the rational parameters were obtained as follows: number of jet orifices N = 3, diameter of jet orifice d = 2.0 mm and angel of jet orifice ??= 75°. An increase in the number of jet orifices constricts free expansion of the injected air among jet streams and keeps them move forward more stably, which causes increases in air density and circumferential velocity component near the wall; however, it is accompanied an increase in the conflict between the jet streams when the number of jet orifices is over large, which decreases yarn suction force. An appropriate diameter of jet orifice promotes the yarn suction force by helping the development of a strong swirling flow and avoiding the occurrence of a normal shock wave. ?The angel of jet orifice plays an important role in generating a swirling flow by controlling the air circumferential velocity component. The yarn suction force has a close relationship to the distribution of air velocity, and depends strongly on the air circumferential velocity component. The normal shock wave should be avoided in the Laval tube when designing the yarn suction gun.